This invention relates to a cable termination. It relates more particularly to method and means for terminating a stranded rope or cable made of wire or other strong material.
Terminals are used at the ends of wire rope and cable to securely connect the cable to an end fitting of some kind. The end fitting may be an eye, a stud, a fork or some other type of link for connecting the rope to an object of a mooring point. Such terminated ropes and cables are widely used in the boating industry, for example, to secure spars and masts. They are also used in a variety or other applications such as to support elevators, move aircraft control flaps, as guy lines, etc.
There are several types of conventional cable terminations. Some terminals are swagged onto the ends of cables. The so-called hot socket terminal in installed on the end of the cable, the cable wires are broomed out and molten zinc is poured into the terminal to form an incompressible plug which retains the cable wires in the terminal. There is also the swageless terminal comprising a split ring engaged over the cable and threaded male and female members which when threaded together clamp the ring against the cable.
All of these conventional terminations have serious drawbacks. The first two types require special tools and equipment in order to secure the terminal to the cable. Therefore, those terminals cannot easily be installed in the field. Rather, the terminated cable must be made to order at the plant. Elevator cables are a particular case in point. These soft core cables are made up of many smaller strands wound together. Each of these strands is, in turn, made up of a multiplicity of still smaller spirally wound wires. Further, the core of the cable consists of a soft lubricating rope. Because of the many wires involved, and the soft core it is quite difficult to anchor the fitting to the cable. Extremely high swagging pressures must be applied to the terminal or the hot socket approach used, both of which can only be done at the factory. This means that elevator cables must be essentially custom-made and brought to the site. If the cable tends to be an inch too long or too short it cannot be used and a new cable must be made up, requiring added time and expense.
The swaged and swageless terminals also can become corroded due to the moisture accumulation in the terminal or due to electrolytic action. This is particularly true if the cable is used in boating or underwater applications where salt water is present. Also in winter, sometimes water inside the terminal freezes to ice, expanding in the process and cracking the terminal. Further in the case of the swaged terminals, the outside cable strands can be damaged during installation by the swagging force applied to the terminal.
Relatively recently there has been developed cable terminals which terminal utilize epoxy resin as the medium for retaining the wires in the terminal. These terminals are advantaged in that they can be installed in the field because the epoxy resin will set without requiring an appreciably applied heat.
This type of terminal is similar to the hot socket terminal in that it comprises a conical sleeve which is engaged over the end of the rope. The end of the rope is then broomed out and epoxy resin is poured into the open end of the socket and surrounds the rope wires. The resin sets up around the wires into a solid wedge-shaped block which tends to retain the rope in the sleeve when tensile stress is applied to the rope. Examples of this type of termination are disclosed in U.S. Pat. Nos. 3,507,949 and 3,468,569.
These prior "cold socket" terminals while sometimes reputed to be able to withstand a tensile stress at least equal to the tensile strength of the rope, do not, in fact, consistently do so. The main reason for this is that when the rope is tensioned, the load is not distributed evenly among the wires inside the terminal sleeve. Consequently some of the wires break or pull out of the resin plug thereby weakening the termination particularly when there are not very many wires in the rope.
The reasons why some wires in the terminal carry more load then others are believed to be three-fold. First, when the end of the rope is broomed out to accept the epoxy resin, this is done without any design so that the wires are not uniformly distributed across the terminal, particularly when the rope is composed of relatively few wires (e.g. 1 .times. 7, 7 .times. 7 or 7 .times. 19 rope). Secondly, when the wires are broomed out in that abrupt fashion, they are deformed from their performed sinuous shape so that individual wires have unnatural crooks and bends which become points of weakness when the rope is under load. Finally, when the resin is poured into the terminal, air bubbles are entrained therein. Consequently when the resin sets, there may be relatively large voids in the resin plug so that the plug does not securely grip all the wires uniformly. The upshot of all this is that the tensile stress rating of these prior end fittings and terminals typified by the ones in the above patents depends primarily on the strength of the mechanical connection or bond between the resin and the rope wires and not on any wedging action between the conical resin plug and sleeve. As often as not, then, when the rope is tensioned, the rope wires out of the terminal before the rope parts.
All of the aforesaid problems plague the terminated stranded wire rope and cable in use today and as a result such terminated cables are quite expensive to make and install and have a relatively short life.